Method and apparatus for testing dielectric adequacy and for indicating physical defects in a nonconducting material

ABSTRACT

An elastomer impregnated with carbon is utilized in conjunction with a conductor to test the dielectric adequacy of a nonconductor and to indicate physical defects, such as cracks, pinholes or a thickness below a predetermined minimum, by depositing traces of carbon on the nonconductor in the area of the defect or the area where the thickness is below the predetermined minimum.

BACKGROUND OF THE INVENTION

This invention relates to a method and apparatus for testingnonconductive materials and particularly to testing fiber reinforcedresin materials for physical and electrical soundness.

Trucks carrying an articulated aerial device or a boom for lifting aman-carrying bucket or basket are often positioned in the proximity ofhigh-voltage power lines and are intended to insulate men located in thebaskets from ground or from other nearby high-voltage lines should theboom or basket inadvertently touch some high-voltage line or a groundwire.

To insure the dielectric adequacy of the basket and boom, it isdesirable to check the conductivity of the basket and boom; however,electrical shock is not the only danger to which men working in basketsare subjected. There can be latent structural defects in the boom orbasket, which will cause it to fail and it is known that sunlight has adeleterious effect on plastic resins, which will cause a gradualdegradation of the physical properties or strength of the material.Thus, apparatus and methods for testing the dielectric adequacy, as wellas structural soundness of such booms and baskets are a necessity toinsure the safety of those who utilize this equipment to maintain thepower lines.

SUMMARY OF THE INVENTION

In general, the method and apparatus utilized to test a nonconductor fordielectric adequacy and for physical defects when made in accordancewith this invention, comprises utilizing an elastomer impregnated orfilled with particulate conducting material as a first conductor inconjunction with a second conductor, the conductors being such that theyare in intimate contact with the material to be tested and imposing a DCvoltage across the conductors and increasing the voltage at a linearrate to a predetermined value, indicating the voltage as it is increasedand indicating the current as the voltage increases. This invention alsoincorporates responding to a nonlinear increase in the rate of increaseof current relative to a linear increase in voltage to decrease the rateat which the voltage is increased and continuing to increase the voltageat a much slower rate until there is a visible mark on the nonconductoroutlining a defect or a smudge appears indicating a thickness below aminimum predetermined thickness.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of this invention will become more apparentfrom reading the following detailed description in connection with theaccompanying drawings, in which corresponding reference charactersindicate corresponding portions throughout the drawings and in which:

FIG. 1 is an elevational view of a boom and basket mounted on a truckindicating typical equipment that may be tested utilizing the apparatusand method described in this invention;

FIG. 2 is a plan view of a belt utilized as an electrode in thisinvention;

FIG. 3 is a sectional view taken on line III--III of FIG. 2;

FIG. 4 is a schematic drawing of apparatus made in accordance with thisinvention for testing a portion of a boom;

FIG. 5 is a schematic drawing of apparatus made in accordance with thisinvention for testing a portion of a boom for physical defects;

FIG. 6 is a plan view of a conductive wand utilized in this invention;

FIG. 7 is a partial sectional view taken on line VII--VII of FIG. 6;

FIG. 8 is a schematic drawing of apparatus made in accordance with thisinvention for testing the dielectric adequacy and the physical soundnessof a basket;

FIG. 9 is a schematic drawing of apparatus made in accordance with thisinvention for testing a nonconductor for dielectric adequacy and forphysical defects;

FIG. 10 is a schematic drawing of apparatus made in accordance with thisinvention and utilized to test a nonconductor for dielectric adequacyand for physical defects.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, and in particular to FIG. 1, there isshown a truck 1 having a boom or articulated aerial device 3 to which abucket, basket, vessel or cockpit 5, which is suitable for transportinga man, is pivotally attached. Such devices are commonly utilized byutility companies to raise workmen to elevated positions to work onpoles, light standards, transformers, electrical lines and/or otherelevated devices. While this invention is particularly applicable totesting such devices for dielectric adequacy and for physical defects,it is not limited thereto, but may be utilized to test any generallynonconductive material, one particular type of material being a fibrousreinforced material commonly referred to as fiberglass. However, theinvention is not limited to testing this particular material but may beutilized on any nonconducting material.

As shown in FIGS. 4 through 10, the testing apparatus comprises a firstconductor or electrode 7, 7a or 7b and a second conductor or electrode9, 9a, 9b or 9c. As shown in these schematic drawings, the testingapparatus also comprises a DC source capable of producing a variable DCvoltage, which generally varies between 0 and 100,000 volts or higherand is indicated schematically by the battery symbol 11 and a variableresistor 13, a DC voltage meter 15 or other means for indicating thevoltage produced by the power source, and a DC amp meter 17 capable ofindicating current in micro- and/or milliampere ranges. Some type ofprotective device, such as a circuit breaker, indicated at 19 is alsoincorporated in the power supply and limits the flow of current in thetest circuit. The electrodes 7 and 9, as shown in FIGS. 2 and 3, areformed from belts or strips of elastomer material filled with aparticulate conducting material, such as carbon. The strips preferablyhave rounded ends 21 and are folded in half. A pair of D-shaped buckles23 are disposed adjacent the fold and the overlapping portions of thestrips are bonded together by an adhesive or other means to form anelastomer belt, which may be pulled tight and buckled in place. Theelectrodes 7a and 9a are ionic solutions capable of conducting anelectrical current and may comprise a plate 24 to provide a largecontact surface within the ionic fluid. The electrodes or conductors 7band 9b are pads which generally conform to the shape of thenonconductor. They may be elastomer pads filled with particulateconducting material; or they may be felt pads, cloth or paper pads,saturated with an ionic solution.

The electrode 9c, as shown in FIGS. 6 and 7, comprises an elastomerstrip impregnated or filled with particulate conducting material, suchas carbon, fastened to a nonconducting handle 25 in such a way as toform a wiper blade 27. The wiper blade 27 is generally a rectangularshaped slab of elastomer material impregnated with carbon clamped by apair of flat bars 29 which are disposed along one longitudinal margin ofthe wiper blade 27. A machine screw 30 or other clamping devicecooperates with a pair of clamping bars 31 to connect the flat bars 29to the handle 25, providing a hand-held wiper or wand 27, which may bewiped across the object to be tested. An insulated wire 33 passesthrough the handle and is electrically connected to the wiper blade 27through the clamping means 31 and flat bars 29.

A method for utilizing the apparatus hereinbefore described to test anonconducting material for dielectric adequacy and for physical defects,such as pinholes, cracks and inclusion of conductive material, generallycomprises the following steps:

placing the first conductor 7, 7a, or 7b adjacent the nonconductor;

placing the second conductor 9, 9a, 9b or 9c adjacent the nonconductorin a spaced relationship with the first conductor, depending on theshape of the nonconductor different types of conductors would beutilized. For beams of rectangular, triangular, round or other regularcross-section, the elastomer belts 7 and 9, as shown in FIG. 2 and 3,are preferred. Whereas to check baskets, boats or other vehicles, theconductors may comprise an ionic solution, such as indicated in FIGS. 8and 9 or a felt cloth or paper pad which conforms to the irregular shapeand is saturated with an ionic solution, as indicated in FIG. 10, mayalso be utilized. The wipers 27, as shown in FIG. 6 and 7, could beutilized with any of the above and the wiper could be shaped for aparticular purpose.

The steps further comprise connecting individually leads or lines from avariable DC voltage power source capable of producing from 0 to 100,000volts or higher to each conductor, one of the leads also being grounded;

generally increasing the DC voltage between the conductor toapproximately 100,000 volts or some predetermined value, depending onthe nonconductor and the relative location of the conductors, linearlyor at a predetermined generally constant rate, for example, increasingfrom 0 to 100,000 volts in thirty seconds;

indicating the DC voltage between the conductors as the voltage isincreased utilizing the voltage meter 15;

indicating the current flowing between the conductors by utilizing theamp meter 17;

holding the voltage at the predetermined level for a specific period oftime, for example, three minutes to indicate the dielectric adequacy ofthe nonconductor;

responding to a nonlinear increase in current relative to a linearincrease in voltage to decrease the rate at which the voltage isincreased, whereby the voltage is increased at a much slower rate untilthere is a visible mark on the nonconductor which generally outlines thedefect, the mark being made by the filler material.

This invention also includes a method for testing the nonconductiveportion of an articulating arm or boom of an aerial lift truck andcomprises the steps of:

placing a first conducting belt 7 around the boom adjacent one endthereof;

pulling the belt tight so that it is in intimate contact with the boom;

buckling the belt so that it doesn't slip and loosen;

placing a second conducting belt 9 around the boom adjacent the otherend thereof;

pulling the belt 9a tight so that it is in intimate contact with theboom;

buckling the belt so that it does not loosen and slip;

connecting individual leads from a variable DC voltage supply capable ofsupplying 0 to 100,000 volts DC or more to the belts 7 and 9;

grounding the truck, one belt and one of the leads from the DC supply;

increasing the voltage between the belts at a generally linear rateuntil it reaches some predetermined voltage, for example, from 0 to100,000 volts in thirty seconds;

leaving the voltage at the predetermined level for a predetermined timeinterval, approximately three minutes;

reducing the voltage to 0 and grounding the belts;

then moving one of the belts so that it is generally parallel to theother belt and a short distance therefrom, approximately 18 inches;

connecting the leads from the DC power supply to the belts;

increasing the DC voltage between the belts to a predetermined value ata generally linear rate;

indicating the voltage as it is being increased;

indicating the current as the voltage is being increased;

responding to a nonlinear increase in the rate at which the currentincreases relative to a linear increase in voltage to decrease the rateat which the voltage is increased;

continuing to increase the DC voltage at a reduced rate until a markappears on the nonconductive boom, the mark indicating the outline andlocation of a physical defect;

successively reducing the voltage across the belts to 0;

grounding the belts and moving at least one belt at a time so as tocheck each incremental portion of the boom by increasing the voltage ata linear rate to a predetermined voltage and responding to a nonlinearincrease in current flowing between the electrodes or belts to reducethe rate at which the voltage is increased and increasing the voltage atthe much lower rate until a mark appears on the boom, indicating theoutline and location of a defect within that portion of the boom.

This invention also incorporates a method for testing a container fordielectric adequacy and for physical defects and comprises the step of:

placing an ionic solution in the container so that it fills at least aportion thereof;

placing a first electrode in the solution;

connecting a supply of DC voltage to the first and to a secondelectrode, the second electrode also being connected to ground andhaving a wiper blade formed from an elastomer filled with a conductiveparticulate conductor material;

imposing a predetermined DC voltage across the electrodes;

passing the wiper portion of the second electrode over the outer side ofthat portion of the container containing the ionic solution;

whereby the particulate material in the wiper electrode will leave marksoutlining physical defects and smudges in the area where the thicknessis below a predetermined value;

raising the container and passing the wiper portion of the secondelectrode over the lower portion thereof;

supporting the lower portion of the container so that it may be filledwith ionic solution and passing the wiper portion of the secondelectrode over the outer portion of that portion of the containercontaining the ionic fluid, whereby the particulate material from thewiper blade will deposit on the surface of the container and outline ofthe physical defects and make smudges where the thickness thereof isbelow a predetermined value.

The method described above for testing a container is intended toinclude any container, a basket for an aerial lift truck, boat hull, anamusement vehicle or cockpit, or any other container or shape which willhold a liquid and is made from a nonconductive material where it isdesirable to test for either dielectric adequacy and/or for physicaldefects or for a minimum thickness.

This invention also includes a method for testing a plastic or resinousmaterial for deterioration due to exposure to sunlight and otheratmospheric conditions, including the steps of:

placing a first conductor which generally conforms to the area to betested on one side of this area. The first conductor may be an ionicsolution as shown in FIG. 8, or as shown in FIG. 10 it may be anelastomer filled with a particulate conductor, such as carbon, or thefirst conductor may be an absorbent pad, such as felt, cloth or paper,saturated with the ionic solution so long as it generally conforms tothe shape of the area to be tested;

connecting the first conductor and a conductor having a wiper blade to aDC power source;

imposing a predetermined DC voltage across the first conductor and thewiper blade;

passing the wiper blade over the area to be tested, whereby marks willappear outlining physical defects and smudges will appear in areas wherethe thickness is below a minimum value;

if no physical defects appear, then reducing the voltage to 0 andgrounding the wiper and the first conductor;

placing another or third conductor, which generally conforms to the areato be tested, on the side opposite the one side having the firstconductor, the third conductor may be an ionic solution as shown in FIG.9, or as shown in FIG. 10 an elastomer filled with a conductor or anabsorbent pad saturated with an ionic solution;

applying a predetermined DC voltage across the conductors and recordingthe current flowing therebetween;

utilizing the plastic or resinous material whereby it is exposed tosunlight or other atmospheric conditions, then after a certain timeinterval, which may be as long as a year or more, retesting the plasticor resinous material by placing the first conductor, which generallyconforms to the area to be tested on one side of the area;

connecting the first conductor and a conductor having a wiper blade to aDC power source;

imposing a predetermined DC voltage across the first conductor and thewiper blade;

passing the wiper blade over the area to be tested, whereby marks willappear outlining physical defects;

if no physical defects are present, placing a third conductor whichgenerally conforms to the area to be tested on the side opposite the oneside having the first conductor;

applying a predetermined DC voltage across the conductors;

recording the current flowing therebetween;

comparing this latest reading with the previous reading, the amount ofcurrent flowing between the conductors being an indication of thedeterioration of the dielectric properties of the plastic or resinousmaterial due to exposure to sunlight and other atmospheric conditionswhich is also an indication of the deterioration of the physicalproperties, such as strength and ductility of the plastic or resinousmaterial so that when the current flowing between the electrodes reachessome predetermined level, the physical properties of the material havereached a level that the material is no longer safe for use or continuedexposure to sunlight and other atmospheric conditions, will soon renderit unsafe for use.

The method and apparatus hereinbefore described advantageously testsnonconductive material for dielectric adequacy, physical defects, suchas cracks, pinholes, inclusion of conductive material, and a thicknessbelow a minimum amount, and these methods and apparatus can also beutilized to indicate the degradation of the physical properties such asthe strength and ductility of the material due to its exposure tosunlight and other atmospheric conditions by making comparisons of thechanges in the dielectric characteristics of the material due to thisexposure. The nondestructive tests hereinbefore described assure thephysical and dielectric adequacy of resinous and plastic materialsutilized to carry men for work or pleasure.

What is claimed is:
 1. A method for testing a nonconductor fordielectric adequacy and for physical defects comprising the stepsof:placing a first conductor adjacent said nonconductor; placing asecond conductor adjacent said nonconductor and in a spaced relationshipwith said first conductor; connecting individual leads from a variableDC voltage power source to each of said conductors; increasing the DCvoltage between said conductors to some predetermined value; indicatingthe voltage between said conductors as the voltage is increased;indicating the current flowing between said conductors as said voltageis increased; responding to a nonlinear increase in the rate of increaseof the current relative to a linear increase in the rate of voltage todecrease the rate at which the voltage is increased; continuing toincrease the voltage at a much lower rate until there is a visible markon the nonconductor outlining the defect.
 2. The method as set forth inclaim 1, wherein the step of placing a first conductor includes placinga first conductor made of an elastomer material and having particulateconducting material disposed therein.
 3. The method as set forth inclaim 2, wherein the step of placing the second conductor includesplacing a second conductor made of an elastomer material and having aparticulate conducting material dispersed therein.
 4. The method as setforth in claim 1, wherein the step of placing a first conductor includesplacing a first conductor so that it is in intimate contact with thenonconductive material being tested.
 5. The method as set forth in claim4, wherein the step of placing the second conductor includes placing thesecond conductor so that it is in intimate contact with thenonconducting material.
 6. A method for testing a nonconductive portionof an articulated nonconducting arm of an aerial lift device for liftingworkmen to an elevated position comprising the steps of:placing a firstconducting belt around the nonconductive arm and adjacent one endthereof; placing a second conducting belt around the nonconducting armadjacent the other end thereof; connecting a variable DC voltage supplyto said belts; increasing the voltage between said belts to somepredetermined value; maintaining said voltage for a predetermined timeinterval, reducing the voltage to 0; grounding said belts; moving one ofsaid belts so that it is disposed a short distance from the other belt;connecting the variable DC voltage supply to said belts; increasing thevoltage between said belts to some predetermined value at a generallylinear rate; indicating the voltage as it is being increased; indicatingthe current flowing between the belts as the voltage between the beltsis increased at a linear rate; responding to a nonlinear increase in therate at which the current increases relative to a linear increase involtage to decrease the rate at which the voltage is increased; andincreasing the voltage at a reduced rate until a mark appears on thenonconductive material outlining the defect.
 7. The method as set forthin claim 6, and further comprising the steps of:successively reducingthe voltage across the belts to 0; grounding the belts; successivelymoving the belts over the arm in small incremental distances;successively increasing the voltage across the belts at a linear rate;indicating the voltage and current as the voltage is increased; andresponding to a nonlinear increase in current relative to a linearincrease in voltage to reduce the rate of increase of voltage;increasing the voltage at the lower rate until a mark outlining anydefect appears on the nonconductive arm.